package cn.fay.chapter18;

import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
/**
 * 对映射文件的部分加锁
 * @author emellend
 *
 */
public class LockingMappedFiles {

	static final int LENGTH=0X8FFFFFF;
	static FileChannel fc;
	
	public static class LockAndModify extends Thread{
		private ByteBuffer buffer;
		private int start,end;

		public LockAndModify(ByteBuffer mbb, int start, int end) {
			this.start = start;
			this.end = end;
			mbb.limit(end);
			mbb.position(start);
			buffer=mbb.slice();
			start();
		}

		public void run() {
			try {
				FileLock lock = fc.lock(start, end, false);
				System.out.println("Locked: "+start+" to "+end);
				while (buffer.position()<buffer.limit()-1) {
					buffer.put((byte) (buffer.get()+1));
				}
				lock.release();
				System.out.println("Released: "+start+" to "+end);
			} catch (Exception e) {
				throw new RuntimeException(e);
			}
		}
	}
	public static void main(String[] args) throws Exception {
		fc = new RandomAccessFile("test.dat", "rw").getChannel();
		MappedByteBuffer out = fc.map(FileChannel.MapMode.READ_WRITE, 0, LENGTH);
		for (int i = 0; i < LENGTH; i++) {
			out.put((byte) 'x');
		}
		new LockAndModify(out, 0, 0+LENGTH/3);
		new LockAndModify(out, LENGTH/2, LENGTH/2+LENGTH/4);
	}
}
